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XxVE
Background: Know: control and data tables , Prerequisites - host, interface , Recognize: RMON Host Group Anticipates: "good packets" xxTE, device discovery xxN8 Host discovery & monitoring Although RMON uses the SNMP protocol, RMON MIBs contain more information than MIB-2 and are often only partially implemented by equipment manufacturers. A minimal RMON agent implementation may support only statistics, history, alarm, and event. RMON MIBs contain Control Tables and Data Tables. The control table table contains entries for sharing of the RMON data table. These entries include index, owner and status rows. The Host RMON 1 MIB group contains Layer 2 statistics associated with each host discovered on the network. Hosts are discovered by passively observing the source and destination MAC addresses as they pass through network equipment with RMON software running. Sometimes dedicated RMON probes are also added to the network to discover hosts passively, and to record other RMON paramters. Only MAC addresses in "good" packets are recorded, MAC addresses from "bad" packets are discarded. Good packets are defined as error-free and having a valid frame length do not meet that criteria. Wiki page The Good, the bad and the RMON describes this in more detail. The RMON Host group is useful to network managers who need to know what the sources and destinations of traffic flows are. This information can assist in fault, security and performance management. In addition to discovering hosts, the Hosts group provides statistics on bandwidth utilisation (packets in, packets out, octets in, octets out), errors (errors out), and volume of broadcast and multicast traffic. The Host MIB is described in RFC2819 as follows: : The host group contains statistics associated with each host discovered on the network. This group discovers hosts on the network by keeping a list of source and destination MAC Addresses seen in good packets promiscuously received from the network. This group consists of the hostControlTable, the hostTable, and the hostTimeTable. The Host group is part of RMON 1 (groups 1 to 10 in the map below). The host The Host group consists of the following tables: hostControlTable, hostTable, hostTimeTable,hostControl2Table. For each interface specified by a row in the hostControlTable there is a row in the hostTable for each MAC address discovered on the interface. 'hostControlTable ' 'hostTable and hostTimeTable' For each interface specified in the hostControlTable, the hostTable contains one row for each MAC (medium access control) address discovered on that interface. hostTimeTable contains exactly the same information, row by row, as hostTable, but the hosts are sorted by time-of-creation order rather than by host MAC Address. This table has two important uses: *Fast download of this potentially large table, since its size is known *Efficient discovery by the management station of new entries in the table, since they will be added at the end of the current table. 'hostControl2Table' hostControl2Table is part of the RMON extension and gives additional information of dropped frames not counted in the statsDropEvents See also RMON Wikipedia entry http://en.wikipedia.org/wiki/RMON RFC2819 http://tools.ietf.org/html/rfc2819#page-6 External Links Tivoli Netcool System Service Monitors, Version 4 RMON1 MIB Group Category:All